This invention relates to a vibration isolating device for supporting a power unit, mainly an automotive engine, etc. or another vibration generating bodies.
As a vibration-proof device for supporting a vibration generator such as an automotive engine so as not to transmit its vibrations to a vehicle body, etc., there are proposed vibration-proof devices having a variety of structures and configurations, whose fundamental construction is such that a vibration generator side member and a vehicle body side member are coupled by a rubber elastomer as a vibration isolator interconnected between them and the vibration generator side member is supported in a vibration-proof manner by the rubber elastomer, for example, a non-liquid-sealed type of one availing oneself of characteristics of the rubber elastomer only to damp the vibrations, a liquid-sealed type of one, wherein liquid is filled within the main body to avail oneself of liquid fluidization effect of an orifice, etc. (cf. e.g. JP Patent Application Publication H10-220508 A, JP Patent Application Publication 2001-280404A).
A vibration-proof device in FIG. 6 is a vibration isolating device pertaining to a comparative example, which it is possible to use so as to support a power unit such as an automotive engine at its lateral position. The device comprises a cylindrical main body fitting 101, a boss fitting 102 disposed rather upwardly of it in the axis center part and to be coupled to a vibration generator side, a rubber elastomer 103 as a vibration isolator interposed between the cylindrical main body fitting 101 and the boss fitting 102 in a manner coupling both, a coupling member 104 with a vibration generator to be secured to the upside of the boss fitting 102, a stopper rubber 105 attached to the coupling member 104, and an arch-shaped stopper member 107 to be fixed to a vehicle body side in forward and rearward parts of the device and positioned while holding a required distance from the stopper rubber 105 in its front and rear parts and upper part, wherein it is constructed so that the rubber elastomer 103 may absorb and damp vibrations from the engine and the stopper rubber 105 may abut on the stopper member 107 thereby regulating a large displacement in the fore-and-aft direction and the upward direction.
In the aforementioned vibration isolating device, front and rear rubber portions 151, 152 of the stopper rubber 105 serve to abut on the stopper member 107 in response to displacements in the fore-and-aft direction of the vibration generator side, thereby performing a stopper action regulating a further greater displacement. Upon running, however, due to the fact that the stopper rubber 105 abuts on the stopper member 107, the dynamic spring constant in the fore-and-aft direction is apt to become high and there is a tendency that a damping effect mainly to vibrations with a relatively small amplitude cannot be sufficiently obtained.
In particular, upon acceleration or running of a vehicle at such a high speed that engine revolution is on the order of 2500 rpm to 4000 rpm, the coupling member 104 at the vibration generator side is displaced rearwards and the rear rubber portion 152 of the stopper rubber 105 remains abutting on the stopper member 107. As a consequence, upon acceleration or running at high speed of a vehicle such as an automobile, vibrations and noise at the vibration generator side are liable to be transmitted to the vehicle body side, with the result that the indoor noise becomes large.
Yet, varying the characteristics of the stopper rubber 105 such as elastic force by the change of material will result in diminishing a spring force upon stopper action and is likely to impair the stopper action and durability.
Stated another way, it is desired in the aforementioned vibration isolating device that the degree of initial abutment of the stopper rubber 105 on the stopper member 107 be relatively soft such that the dynamic spring constant in the fore-and-aft direction can be reduced and the stopper action can be reliably performed; and that upon acceleration or running at high speed of a vehicle, the transmission of noise to the vehicle body side can be suppressed.